cmd/internal/obj/arm64: Emit UDF instruction for undefined Prog nodes

UDF provides a stronger guarantee for generating the Undefined
Instruction exception than the current value being emitted.

Change-Id: I234cd70ce04f21311959c1061ae24992438105f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/605155
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

diff --git a/src/cmd/internal/obj/arm64/asm7.go b/src/cmd/internal/obj/arm64/asm7.go
index 178c83c0bc693847a564ba2b11e42413197ed770..bd2bd037ba850cd5380dfa178a50a87bedeefd03 100644 (file)
--- a/src/cmd/internal/obj/arm64/asm7.go
+++ b/src/cmd/internal/obj/arm64/asm7.go
@@ -5338,10 +5338,10 @@ func (c *ctxt7) asmout(p *obj.Prog, o *Optab, out []uint32) {
        // This is supposed to be something that stops execution.
        // It's not supposed to be reached, ever, but if it is, we'd
        // like to be able to tell how we got there. Assemble as
-       // 0xbea71700 which is guaranteed to raise undefined instruction
+       // UDF which is guaranteed to raise the undefined instruction
        // exception.
        case 90:
-               o1 = 0xbea71700
+               o1 = 0x0
 
        case 91: /* prfm imm(Rn), <prfop | $imm5> */
                imm := uint32(p.From.Offset)